.\" Copyright (c) 2018 Conrad Meyer <cem@FreeBSD.org>
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.Dd February 10, 2018
.Dt SYSCALL_HELPER_REGISTER 9
.Os
.Sh NAME
.Nm syscall_helper_register ,
.Nm syscall_helper_unregister
.Nd kernel syscall registration routines
.\"
.Sh SYNOPSIS
.In sys/sysent.h
.Ft int
.Fn syscall_helper_register "struct syscall_helper_data *sd" "int flags"
.Ft int
.Fn syscall_helper_unregister "struct syscall_helper_data *sd"
.\"
.Ss INITIALIZER MACROS
.Ft struct syscall_helper_data
.Fn SYSCALL_INIT_HELPER "syscallname"
.Ft struct syscall_helper_data
.Fn SYSCALL_INIT_HELPER_F "syscallname" "int flags"
.\"
.Ss COMPATIBILITY INITIALIZER MACROS
.Ft struct syscall_helper_data
.Fn SYSCALL_INIT_HELPER_COMPAT "syscallname"
.Ft struct syscall_helper_data
.Fn SYSCALL_INIT_HELPER_COMPAT_F "syscallname" "int flags"
.\"
.Sh DESCRIPTION
The
.Fn syscall_helper_register
registers a system call.
This function takes the structure
.Va struct syscall_helper_data sd ,
which specifies the parameters for syscall registration:
.Pp
.Bd -literal -offset indent -compact
struct syscall_helper_data {
	struct sysent	new_sysent;
	struct sysent	old_sysent;
	int		syscall_no;
	int		registered;
};
.Ed
.Pp
The only valid flag for the
.Fa flags
argument to
.Fn syscall_helper_register
is
.Dv SY_THR_STATIC .
This flag prevents the syscall from being unregistered.
.\"
.Pp
Before use, the structure must be initialized with one of the
.Fn SYSCALL_INIT_HELPER*
macros.
In new code, syscall implementation functions shall be named
.Fn sys_syscallname
and the regular macros shall be used.
.Pp
For legacy syscall functions named without "sys_" prefixes, the "COMPAT"
versions of the macros may be used.
.Pp
The only valid flag for the
.Fa flags
argument to the "F" variants of the initializer macros is
.Dv SYF_CAPENABLED .
This flag indicates that the syscall is allowed in capability mode.
.Pp
The
.Fn syscall_helper_unregister
unregisters a system call.
This function takes the same structure
.Va struct syscall_helper_data sd
that was previously initialized in the manner described above and used in a
successful invocation of
.Fn syscall_helper_register .
.\"
.Sh RETURN VALUES
If successful,
.Fn syscall_helper_register
and
.Fn syscall_helper_unregister
will return 0.
Otherwise, they will return an error.
.\"
.Sh ERRORS
The
.Fn syscall_helper_register
call will fail and the syscall will not be registered if:
.Bl -tag -width Er
.It Bq Er EINVAL
The
.Fa flags
argument contained a value other than
.Dv SY_THR_STATIC .
.It Bq Er EINVAL
The specified syscall number,
.Dv sd.syscall_no
.Dv ( SYS_syscallname ) ,
was outside of the valid range of system call numbers (zero through
.Dv SYS_MAXSYSCALL ) .
.It Bq Er ENFILE
The system call table does not have any available slots.
.It Bq Er EEXIST
The specified syscall number,
.Dv sd.syscall_no
.Dv ( SYS_syscallname ) ,
was already in use.
.El
.\"
.Sh SEE ALSO
.Xr SYSCALL_MODULE 9
